The association of reinforcement fibers and organic material to achieve a finished composite product can be performed in many ways. This composite product should exhibit in particular the properties required for the contemplated application. Its properties, in particular its mechanical properties, are a function of the quality of the bond that exists between the organic material and the fibers that reinforce it. One of the numerous means contributing to obtaining this result is the prior coating of the fibers with an organic material identical, or at the very least compatible, with that which will form the mass of the finished product. There are numerous methods for coating reinforcement fibers which are used independently of the process of producing said fibers. These coating methods require an additional operation and have, among other drawbacks, that of increasing the production cost of the yarn.
To avoid the drawbacks of the indirect processes, other processes advocate coating the fibers at the time of their production. These direct processes are inspired by the means traditionally used to coat the surface of fibers with a finish. The device for application of this finish is installed in the path traveled by the fibers between their forming zone and the zone where they are collected in one form or another.
U.S. Pat. No. 4,537,610, relating to the production of continuous glass fibers, describes an installation which is exemplary in this regard. A die, heated by Joule effect, is fed molten glass streams which flow through a multiplicity of orifices placed at the base of the die. The streams, after mechanical drawing, give rise to a multiplicity of continuous fibers which are assembled in a single yarn. A coating device is installed between the base of the die and the point of assembling the fibers. This device comprises a tank, fed with a thermoplastic organic mixture in the molten state, and a roller which is partially immersed in the organic material and partially in contact with the advancing fibers. The roller, in rotation around its axis, drives on its surface an organic film picked up by the fibers during their passage. This type of process, although advantageous, still exhibits a certain number of constraints.
It would be advantageous to obtain directly a composite yarn in which the amount of organic material is high relative to the weight of said yarn. According to direct processes known at present, the weight by percent of the organic material retained by the yarn is greater at slower yarn drawing speeds and vice versa.